1. Technical Field
This disclosure relates to an image forming apparatus, and more specifically to an image forming apparatus including a recording head for ejecting liquid droplets and a head tank for supplying liquid to the recording head.
2. Description of the Related Art
Image forming apparatuses are used as printers, facsimile machines, copiers, plotters, or multi-functional devices having two or more of the foregoing capabilities. As one type of image forming apparatus employing a liquid-ejection recording method, inkjet recording apparatuses are known that use a recording head (liquid ejection head or liquid-droplet ejection head) for ejecting droplets of ink or other liquid.
Such inkjet-type image forming apparatuses may have a head tank (also referred to as sub tank) on a recording head to supply ink from an ink cartridge serving as a main tank replaceably mounted on an apparatus body.
For an image forming apparatus having such an ink supply system, when the ink cartridge in an ink end state is replaced, the interior of the ink cartridge is in a negative pressure. Hence, for example, JP-2010-155446-A proposes to feed a desired amount of ink in reverse from the head tank to the ink cartridge and release the negative pressure in the ink cartridge in the ink end state to prevent air from intruding into a liquid feed passage when the ink cartridge is removed for replacement.
However, if ink is fed in reverse from the head tank to the ink cartridge when an ink level of the head tank is low, bubbles may be fed into the liquid feed passage. Even when the ink level of the head tank is not low, bubbles may be fed into the liquid feed passage if bubbles are already included in the head tank.
If bubbles intrude into the liquid feed passage as described above, bubbles may be fed to the head tank when ink is fed from a new ink cartridge to the head tank with art air release valve of the head tank opened. For example, when the ink level of the head tank is detected with electrode pins, bubbles may hamper detection of the ink level. As a result, ink is oversupplied and bubbled ink may intrude into the air release valve, thus causing a failure.
Hence, as described above, when the ink level of the head tank is low or bubbles are likely to intrude into the liquid feed passage, the image forming apparatus does not feed ink in reverse from the head tank to the ink cartridge.
As a result, since the negative pressure in the ink cartridge in the end state cannot be released, the image forming apparatus needs to feed ink based on the assumption that air intrudes into the liquid feed passage after replacement of ink cartridges, thus increasing the liquid feed time and the ink consumption amount.